In the past six years, Ventura County officials have overseen the cleanup of 14 meth labs in homes, a hotel and storage lockers from Meiners Oaks to Thousand Oaks.

"All sites had some level of contamination," said Rick Bandelin, manager of the county's hazardous materials program.

But as more methamphetamine makes its way across the border from Mexico, the number of meth labs found in Ventura County has shrunk, authorities say.

Still, the effects of cooking meth can cause long-term problems. Ingredients from acetone to methanol can leave toxic residue on carpeting, wallpaper and even floorboards.

California legislators passed the Methamphetamine Contaminated Property Cleanup Act of 2005, requiring counties to supervise cleanup efforts and determine if a home is safe to live in.

Law enforcement agencies are supposed to alert the county when a possible meth lab is found. If the site is contaminated, county officials notify property owners, who are required to get and pay for a cleanup. The county takes out a lien on a property until the work is finished.

The state law took effect in 2006, and law enforcement agencies notified the county of six meth labs found that year. Four more were found the following year, and an additional four were found in 2009, county records show.

They were found in or near nearly every city in the county, from densely populated neighborhoods to rural areas.

All had some contamination, mostly limited to one room or an area of the property, Bandelin said. "In one of the sites, the contamination was limited to a plastic table," he said.

California law also requires the property owners to disclose possible contamination to potential buyers or renters.

Karen Heyrend, president elect of the Ventura County Coastal Association of Realtors, said the requirement has had little impact locally. In the past few years, she hasn't heard of any homes with such a disclosure.

"Over the last couple of years ... we're had very few methamphetamine labs," Ventura County sheriff's Sgt. Mike Horne said. Much of the methamphetamine showing up in the county now is brought in from Mexico, he said.

It's a trend throughout the state and nation. A federal report says 92 meth labs or dump sites were found in California in 2011. That's down from a high of 789 sites found in 2004.

Michelle Gregory, a spokeswoman for the California Department of Justice, said the decrease in labs making meth from scratch coincided with several new laws taking effect, including one that made it harder to buy large amounts of medications containing pseudoephedrine, she said. The cold medication can be used in methamphetamine manufacturing.

Authorities, however, are seeing more conversion labs, where meth powder is converted into crystal meth. "Typically, it's easier to move the powder from across the border and convert it here in the U.S.," Gregory said.

And the number of people using methamphetamine in the United States continues to rise, officials said.

In Ventura County, Horne said, his five-person team alone is working on up to 60 meth-related cases at any one time.